class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        int n=nums.size();
        sort(nums.begin(),nums.end());
        vector<vector<int>> ret;
        for(int i=0;i<n;)
        {
            for(int j=i+1;j<n;)
            {
                int left=j+1;
                int right=n-1;
                long long mytarget=(long long)target-nums[i]-nums[j];
                while(left<right)
                {
                    if(nums[left]+nums[right]>mytarget)
                    {
                        right--;
                    }
                    else if(nums[left]+nums[right]<mytarget)
                    {
                        left++;
                    }
                    else
                    {
                        ret.push_back({nums[i],nums[j],nums[left],nums[right]});
                        left++;
                        right--;
                        while(left<right&&nums[left]==nums[left-1])
                        {
                            left++;
                        }
                        while(left<right&&nums[right]==nums[right+1])
                        {
                            right--;
                        }
                    }
                }
                ++j;
                while(j<n&&nums[j]==nums[j-1])
                {
                    ++j;
                }
            }
            ++i;
            while(i<n&&nums[i]==nums[i-1])
            {
                ++i;
            }
        }
        return ret;
    }
};
